The immune systems of some individuals may be capable of resisting HIV infection. These individuals do not appear to be infected with HIV despite multiple sexual encounters with HIV infected partners. This study will examine the immune systems of these individuals to determine what factors are responsible for their ability to resist HIV infection.

Study hypothesis: Some long-term, multiply-exposed seronegative persons have relative resistance to HIV infection maintained by T cell responses.

Rare individuals appear naturally resistant to overt HIV-1 infection despite repeated sexual exposures. These individuals, referred to as exposed seronegatives (ES), represent a unique population in which to evaluate mechanisms by which HIV-1 replication is either controlled or aborted. The purpose of the study is to analyze HIV-specific immune responses, both cellular and humoral, that exist in seronegative individuals who have experienced multiple exposures to HIV by sexual contact.

This study will follow participants for 2 years. Participants will have 25 study visits during the study. Assessments will include HIV tests, viral load measurements, CD4 counts, pregnancy tests, and physical exams.

Inclusion Criteria:

• Good general health
• HIV uninfected
• Repeated exposures to HIV through unprotected sexual intercourse within the 2 years prior to study entry
• Live in the greater Seattle area
• Plan to stay in the greater Seattle area for the 2 years after study entry

Exclusion Criteria:

• Pregnancy